Properties and performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ + Sm0.2Ce0.8O1.9 composite cathode

The properties and performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) + Sm_0.2Ce_0.8O_1.9 (SDC) (70:30 in weight ratio) composite cathode for intermediate-temperature solid-oxide fuel cells were investigated. Mechanical mixing of BSCF with SDC resulted in the adhesion of fine SDC particles to the surface of coarse BSCF grains. XRD, SEM-EDX and O₂-TPD results demonstrated that the phase reaction between BSCF and SDC was negligible, constricted only at the BSCF and SDC interface, and throughout the entire cathode with the formation of new (Ba,Sr,Sm,Ce)(Co,Fe)O_3−δ perovskite phase at a firing temperature of 900, 1000, and ≥ 1050 °C, respectively. The BSCF + SDC electrode sintered at 1000 °C showed an area specific resistance of ∼0.064 Ω cm² at 600 °C, which is a slight improvement over the BSCF (0.099 Ω cm²) owing to the enlarged cathode surface area contributed from the fine SDC particles. A peak power density of 1050 and ∼382 mW cm⁻² was reached at 600 and 500 °C, respectively, for a thin-film electrolyte cell with the BSCF + SDC cathode fired from 1000 °C.     

Enhancing the short-circuit current and efficiency of organic solar cells using MoO3 and CuPc as buffer layers

Efficient bulk-heterojunction (BHJ) (regioregular poly (3-hexylthiophene) (P3HT): (6, 6)-phenyl C₆₁ butyric acid methyl ester (PCBM)) solar cells were fabricated with molybdenum trioxide (MoO₃) and copper phthalocyanine (CuPc) as buffer layers. The insertion of MoO₃ layer was found to be critical to the device performance, effectively extracting holes to prevent the exciton quenching and reducing the interfacial resistance because of alignment of energy levels. The introduction of CuPc buffer layer was observed to be ameliorative for device performance, further enlarging the visible absorption spectra range of the devices. The effect of the MoO₃ and CuPc layer thickness on device performance was studied. The optimized thickness was achieved when MoO₃ layer was 12 nm and CuPc layer was 6 nm, resulting in optimized power conversion efficiency (PCE) of 3.76% under AM1.5G 100 mW/cm² illumination.     

Synthesis and electrochemical performance of the high voltage cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with improved rate capability

The high voltage layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode material, which is a solid solution between Li₂MnO₃ and LiMn_0.4Ni_0.4Co_0.2O₂, has been synthesized by co-precipitation method followed by high temperature annealing at 900 °C. XRD and SEM characterizations proved that the as prepared powder is constituted of small and homogenous particles (100-300 nm), which are seen to enhance the material rate capability. After the initial decay, no obvious capacity fading was observed when cycling the material at different rates. Steady-state reversible capacities of 220 mAh g⁻¹ at 0.2C, 190 mAh g⁻¹ at 1C, 155 mAh g⁻¹ at 5C and 110 mAh g⁻¹ at 20C were achieved in long-term cycle tests within the voltage cutoff limits of 2.5 and 4.8 V at 20 °C.     

The electrochromic and photocatalytic properties of electron beam evaporated vanadium-doped tungsten oxide thin films

The electrochromic and photocatalytic properties of vanadium-doped tungsten trioxide thin films prepared at room temperature (300 K) by the electron beam evaporation technique are reported in this paper. The vanadium to tungsten ratio (V/W) in these films are 0.003, 0.019, 0.029 and 0.047. The optical band gap of the vanadium-doped tungsten oxide (WO₃) thin film initially increases from 3.16 to 3.28 eV for V/W ratio 0.003 then decreases to 3.15 eV for V/W ratio 0.047. These vanadium-doped films switch between neutral gray and transparent states. The coloration efficiency (CE) decreases from 82 cm² C⁻¹ (pure WO₃) to 27 cm² C⁻¹ for the film containing V/W ratio 0.047. The photocatalytic activity has enhanced with vanadium doping and maximum activity of 15% (percentage change in optical density of methylene blue due to photo degradation) has been observed for the film containing V/W ratio of 0.019. The Kelvin probe measurements show that the work function of pure WO₃ films is 4.07 eV and vanadium doping initially increases the work function to 4.19 eV for V/W ratio 0.019 and then decreases it to 3.97 eV for film with V/W ratio 0.047.     

Electrochemical supercapacitor behavior of Ni3(Fe(CN)6)2(H2O) nanoparticles

Nanosized Ni₃(Fe(CN)₆)₂(H₂O) was prepared by a simple co-precipitation method. The electrochemical properties of the sample as the electrode material for supercapacitor were studied by cyclic voltammetry (CV), constant charge/discharge tests and electrochemical impedance spectroscopy (EIS). A specific capacitance of 574.7 F g⁻¹ was obtained at the current density of 0.2 A g⁻¹ in the potential range from 0.3 V to 0.6 V in 1 M KNO₃ electrolyte. Approximately 87.46% of specific discharge capacitance was remained at the current density of 1.4 A g⁻¹ after 1000 cycles.     

Intermediate-to-low temperature protonic ceramic membrane fuel cells with Ba0.5Sr0.5Co0.8Fe0.2O3-δ–BaZr0.1Ce0.7Y0.2O3-δ composite cathode

The perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ–BaZr_0.1Ce_0.7Y_0.2O_3-δ (BSCF–BZCY) composite oxides were synthesized by a modified Pechini method and examined as a novel composite cathode for intermediate-to-low temperature protonic ceramic membrane fuel cells (ILT-PCMFCs). Thin proton-conducting BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) electrolyte and NiO–BaZr_0.1Ce_0.7Y_0.2O_3-δ (NiO–BZCY) anode functional layer were prepared over porous anode substrates composed of NiO–BaZr_0.1Ce_0.7Y_0.2O_3-δ by a one-step dry-pressing/co-firing process. A laboratory-sized quad-layer cell of NiO–BZCY/NiO–BZCY(∼50 μm)/BZCY(∼20 μm)/BSCF–BZCY(∼50 μm) was operated from 550 to 700 °C with humidified hydrogen (∼3% H₂O) as fuel and the static air as oxidant. A high open-circuit potential of 1.009 V, a maximum power density of 418 mW cm⁻², and a low polarization resistance of the electrodes of 0.10 Ω cm² was achieved at 700 °C. These investigations have indicated that proton-conducting BZCY electrolyte with BSCF perovskite cathode is a promising material system for the next generation solid oxide fuel cells (SOFCs).     

Enhanced sinterability of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ by addition of nickel oxide

The effect of nickel oxide addition on the sintering behavior and electrical properties of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb) as an electrolyte for solid oxide fuel cells was systematically studied. Results suggest that the addition of a small amount (∼1 wt%) of NiO to BZCYYb greatly promoted densification, achieving ∼96% of the theoretical density after sintering at 1350 °C in air for 3 h (reducing the sintering temperature by ∼200 °C). Further, a sample sintered at 1450 °C for 3 h showed high open circuit voltages (OCVs) when used as the electrolyte membrane to separate the two electrodes under typical SOFC operating conditions, indicating that the electrical conductivity of the electrical conductivity of the BZCYYb was not adversely affected by the addition of ∼1 wt% NiO.     

Synthesis and characterization of Li3V(2 − 2x/3)Mgx(PO4)3/C cathode material for lithium-ion batteries

Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C (x = 0, 0.15, 0.30, 0.45) composites have been synthesized by the sol-gel assisted solid state method, using adipic acid C₆H₁₀O₄ (hexanedioic acid) as carbon source. The particle size of the composites is ∼1 μm. During the pyrolysis process, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C network structure is formed. The effect of Mg²⁺ doped on the electrochemical properties of Li₃V₂(PO₄)₃/C positive materials has been studied. Li₃V_1.8Mg_0.30(PO₄)₃/C as the cathode materials of Li-ion batteries, the retention rate of discharge capacity is 91.4% (1 C) after 100 cycles. Compared with Li₃V₂(PO₄)₃/C, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C composites have shown enhanced capacity and retention rate capability. The long-term cycles and ex situ XRD tests disclose that Li₃V_1.8Mg_0.30(PO₄)₃ exhibits higher structural stability than the undoped system.     

Lanthanum oxide-coated stainless steel for bipolar plates in solid oxide fuel cells (SOFCs)

Solid oxide fuel cells typically operate at temperatures of about 1000 °C. At these temperatures only ceramic interconnects such as LaCrO₃ can be employed. The development of intermediate-temperature solid oxide fuel cells (IT-SOFCs) can potentially bring about reduced manufacturing costs as it makes possible the use of an inexpensive ferritic stainless steel (STS) interconnector. However, the STS suffers from Cr₂O₃ scale formation and a peeling-off phenomenon at the IT-SOFC operating temperature in an oxidizing atmosphere. Application of an oxidation protective coating is an effective means of providing oxidation resistance. In this study, we coated an oxidation protective layer on ferritic stainless steel using a precursor solution prepared from lanthanum nitrate, ethylene glycol, and nitric acid. Heating the precursor solution at 80 °C yielded a spinable solution for coating. A gel film was coated on a STS substrate by a dip coating technique. At the early stage of the heat-treatment, lanthanum-containing oxides such as La₂O₃ and La₂CrO₆ formed, and as the heat-treatment temperature was increased, an oxidation protective perovskite-type LaCrO₃ layer was produced by the reaction between the lanthanum-containing oxide and the Cr₂O₃ scale on the SUS substrate. As the concentration of La-containing precursor solution was increased, the amount of La₂O₃ and La₂CrO₆ phases was gradually increased. The coating layer, which was prepared from a precursor solution of 0.8 M, was composed of LaCrO₃ and small amounts of (Mn,Cr)O₄ spinel. A relatively dense coating layer without pin-holes was obtained by heating the gel coating layer at 1073 K for 2 h. Microstructures and oxidation behavior of the La₂O₃-coated STS444 were investigated.     

A stable and thin BaCe0.7Nb0.1Gd0.2O3−δ membrane prepared by simple all-solid-state process for SOFC

BaCe_0.7Nb_0.1Gd_0.2O_3−δ (BCNG) and BaCe_0.8Gd_0.2O_3−δ (BCG) were synthesized by solid-state reaction method. The samples obtained were exposed in 3% CO₂ + 3% H₂O + 94% N₂ at 700 °C for 20 h in order to evaluate their chemical stability. It was found that BCNG exhibited adequate chemical stability while BCG decomposed and impurities were observed in the final products. Additionally, the BCNG demonstrated similar behavior as BCG in high-temperature thermal stability and in TEC and displayed a conductivity of 0.007 S cm⁻¹ at 700 °C in humid hydrogen which was slightly lower than BCG (0.009 S cm⁻¹) at the same conditions. Fuel cells with BCNG as electrolyte were successfully fabricated and the thickness of BCNG layer can be easily adjusted as lower as 10 μm by a simple all-solid-state process. The fuel cells exhibited OCV as high as 1.0 V at 700 °C with maximum output power 340 mW cm⁻² and interfacial resistance as low as 0.51 Ω cm².     

Hybrid inverted organic photovoltaic cells based on nanoporous TiO2 films and organic small molecules

Solar cells based on nanoporous TiO₂ films with an inverted structure of indium tin oxide (ITO)/TiO₂/copper phthalocyanine (CuPc):fullerene (C₆₀)/CuPc/poly(3,4-oxyethyleneoxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Au were fabricated. The best overall photovoltaic performance undergoing a series of device optimization was achieved with the device of ITO/dense TiO₂ (30 nm)/nanoporous TiO₂ (130 nm)/C₆₀:CuPc (1:6 weight) (20 nm)/CuPc (20 nm)/PEDOT:PSS (50 nm)/Au (30 nm). The device using the nanoporous TiO₂ films has better photovoltaic properties compared to those using dense TiO₂ films. Higher photovoltaic performances were obtained by introducing a coevaporated layer of C₆₀:CuPc between TiO₂ and CuPc. The stability of inverted structure was better than that of the normal device, which gives a promising way for fabrication of solar cells with improved stability.     

NiMn2O4 spinel as an alternative coating material for metallic interconnects of intermediate temperature solid oxide fuel cells

In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn₂O₄ is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr₂O₃ and an outer layer of doped NiMn₂O₄ and Mn₂O₃; and the growth of Cr₂O₃ and formation of MnCr₂O₄ are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm². The above results indicate that NiMn₂O₄ is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.     

Synthesis and characterization of submicron-sized LiNi1/3Co1/3Mn1/3O2 by a simple self-propagating solid-state metathesis method

Submicron-sized LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials were synthesized using a simple self-propagating solid-state metathesis method with the help of ball milling and the following calcination. A mixture of Li(ac)·2H₂O, Ni(ac)₂·4H₂O, Co(ac)₂·4H₂O, Mn(ac)₂·4H₂O (ac = acetate) and excess H₂C₂O₄·2H₂O was used as starting material without any solvent. XRD analyses indicate that the LiNi_1/3Co_1/3Mn_1/3O₂ materials were formed with typical hexagonal structure. The FESEM images show that the primary particle size of the LiNi_1/3Co_1/3Mn_1/3O₂ materials gradually increases from about 100 nm at 700 °C to 200–500 nm at 950 °C with increasing calcination temperature. Among the synthesized materials, the LiNi_1/3Co_1/3Mn_1/3O₂ material calcined at 900 °C exhibits excellent electrochemical performance. The steady discharge capacities of the material cycled at 1 C (160 mA g⁻¹) rate are at about 140 mAh g⁻¹ after 100 cycles in the voltage range 3–4.5 V (versus Li⁺/Li) and the capacity retention is about 87% at the 350th cycle.     

The pseudo-catalytic promotion of nitric oxide oxidation by ethane at low temperatures

Experimental work carried out in a flow reactor has shown that, from 700 to 750 K, low concentrations of ethane can act as a virtual catalyst in effecting the oxidation of NO to NO₂. That is, while there is strong promotion of the oxidation of NO, there is very little concurrent degradation of the ethane. This contrasts with other experimental and modeling investigations, in which promotion by the hydrocarbon of NO oxidation has accompanied oxidation of a considerable fraction of the hydrocarbon. The rate of this pseudo-catalytic effect is significantly affected by the concentrations of both ethane and oxygen, which in this study ranged from 0 to 70% for [O₂], 0 to 5000 ppm for [C₂H₆], and 0 to 350 ppm for [NO]. The level of reaction achieved under the various conditions was measured in terms of the rates of formation of NO₂ and C₂H₄. Current kinetic mechanisms, though displaying good accuracy in other temperature regimes, fail to predict this pseudo-catalytic behavior of ethane, indicating that several elementary reactions important at the low temperatures are missing or poorly represented in such mechanisms. Mechanistic modifications are discussed and allow the measurements to be simulated more closely than with existing reaction schemes. It has been shown that the relative rates of the competing reactions C₂H₅ + O₂ → C₂H₄ + HO₂ and C₂H₅ + O₂ (+M) → C₂H₅O₂ + (M) are of critical importance in this situation.     

Thermal expansion and electrochemical properties of Ni-doped GdBaCo2O5+δ double-perovskite type oxides

Layered GdBaCo_2 −x Ni_xO_5 + δ (0 ≤ x ≤ 0.3) complex oxides were synthesized and investigated as cathodes for intermediate-temperature solid oxide fuel cell (IT-SOFCs). All compositions formed an orthorhombic double-perovskite structure after calcination at 1000 °C for 5 h. The thermal expansion coefficient (TEC) was effectively decreased due to the partial substitution of Ni for Co, but the cathodic polarization resistance slightly increased with the increasing Ni content. Among the tested oxides, the GdBaCo_1.7Ni_0.3O_5 + δ composition showed a fairly reduced TEC (15.5 × 10⁻⁶ K⁻¹) and reasonably low polarization resistances (e.g., 0.54 Ωcm² at 600 °C), which was considered as a promising candidate for IT-SOFCs.     

Interactions of refractory materials with molten gasifier slags

The current study focuses on the analysis of sessile-drop interfacial reactions between two synthetic slags (based on average ash chemistries of coal and petcoke feedstock) and two refractory materials (90 wt% Cr₂O₃-10 wt% Al₂O₃ and 100 wt% Al₂O₃), using a Confocal Scanning Laser Microscope (CSLM). Ground slag samples (less than 325 mesh) were placed at specific microstructure locations on refractory substrates and heated to 1500 °C in an atmosphere of CO/CO₂ gas mixture (volume ratio = 1.8), using a gold-image heating chamber. Cross-sections of the slag/refractory interface indicated unique slag penetration into preferred areas of the refractory and grain dissolution into the slag which promoted spalling of the refractory. Initially, the slag attacked both grain boundaries and fine microstructure areas, freeing alumina grains into the slag. The formation of VO_x-based crystalline material in the petcoke slag was found to alter the liquid composition. Chemical spalling of Cr-containing crystal layer also facilitated degradation of the refractory.     

Electrochemical profile of an asymmetric supercapacitor using carbon-coated LiTi2(PO4)3 and active carbon electrodes

In this work, we reported an asymmetric supercapacitor in which active carbon (AC) was used as a positive electrode and carbon-coated LiTi₂(PO₄)₃ as a negative electrode in 1 M Li₂SO₄ aqueous electrolyte. The LiTi₂(PO₄)₃/AC hybrid supercapacitor showed a sloping voltage profile from 0.3 to 1.5 V, at an average voltage near 0.9 V, and delivered a capacity of 30 mAh g⁻¹ and an energy density of 27 Wh kg⁻¹ based on the total weight of the active electrode materials. It exhibited a desirable profile and maintained over 85% of its initial energy density after 1000 cycles. The hybrid supercapacitor also exhibited an excellent rate capability, even at a power density of 1000 W kg⁻¹, it had a specific energy 15 Wh kg⁻¹ compared with 24 Wh kg⁻¹ at the power density about 200 W kg⁻¹.     

Preparation of supported SrCeO3-based membrane by spin coating method

SrCe_0.9Y_0.1O_3−δ (SCY10) powder with a pure perovskite phase is prepared by solid-state reaction method. NiO is dispersed uniformly in SCY10 powder to fabricate NiO-SCY10 anode substrate. The starting powder, the mixture of SrCO₃, CeO₂ and Y₂O₃, is deposited directly on the green substrate instead of SCY10 powder by spin coating. After co-firing at 1300 °C for 3 h, the starting powder reacts to form SCY10 top layer on the substrate. SEM micrographs show that the top layer is defect-free and adheres well with the anode substrate without any delamination. A single fuel cell is assembled with anode-supported SCY10 membrane as electrolyte membrane and Ag as cathode. The electrochemical property of the fuel cell is tested with hydrogen as fuel in the temperature range of 600-800 °C. The open circuit voltage (OCV) reaches 1.05 V at 800 °C, and the maximum power density is 50 mW cm⁻², 155 mW cm⁻², 200 mW cm⁻² at 600 °C, 700 °C, 800 °C, respectively.     

Investigation of Sm0.5Sr0.5CoO3−δ/Co3O4 composite cathode for intermediate-temperature solid oxide fuel cells

The electrochemical properties of an Sm_0.5Sr_0.5CoO_3−δ/Co₃O₄ (SSC/Co₃O₄) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co₃O₄ composition, oxygen partial pressure and CO₂ treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co₃O₄ content in the composite cathode was about 40 wt.%. A single cell with this optimized C₄₀-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm², and yielded a maximum power density of 1092 mW cm⁻² with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm⁻² when pure oxygen was used as the oxidant for a cell with a C₃₀-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO₂-treated cathode, also implied promising applications of such highly efficient SSC/Co₃O₄ composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.     

Activity of dealloyed PtCo3 and PtCu3 nanoparticle electrocatalyst for oxygen reduction reaction in polymer electrolyte membrane fuel cell

We report a comparative study of the alloy formation and electrochemical activity of dealloyed PtCo₃ and PtCu₃ nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). For the Pt-Co system the maximum annealing temperatures were 650 °C, 800 °C and 900 °C for 7 h to drive the Pt-Co alloy formation and the particle growth. EDS and XRD were employed for the characterization of catalyst powders. The RDE and RRDE experiments were conducted in 0.1 M HClO₄ at room temperature.We demonstrate that the mass and surface area specific ORR activities of Pt-Co and Pt-Cu alloys after voltammetric activation exhibit a considerable improvement compared to those of pure Pt/C. The dealloyed PtCo₃ (800 °C/7 h) electrocatalyst performs 3 times higher in terms of Pt-based mass activity and 4-5 times higher in terms of ECSA-based specific activity than a 28.2 wt.% Pt/C. Dealloyed Pt-Co catalysts (800 °C/7 h) show the most favorable balance between mass and specific ORR activity with a particle size of 2.2 ± 0.1 nm. We hypothesize that geometric strain effects of the dealloyed Pt-Co nanoparticles, similar to those found in dealloyed PtCu₃ nanoparticles, are responsible for the improvement in ORR activity [1].